You'll have a very hard and reflective interior and with top and bottom parallel and sides parallel. This all leans towards a potential noise problem, IMHO. It would be prudent to allow access to the inside once it's assembled; if nothing else put something down the tube that breaks up the continuous flat surfaces.

Our plastic barrel tube mentioned above had five 45 gallon steel drums joined end to end and with the tops and bottoms removed to form the entry part where the shooter was positioned. We soon had to stick some old carpet on the inside of the oil drums.